One of the examples of a high zoom-ratio zoom lens system of conventional technology is disclosed in Japanese Laid-open Patent Application S58-33531. This zoom lens system has a relatively small back focus for the focal length at the wide-angle end, providing a small back focus with an F-number of F/4 to F/4.5, which is dark. Accordingly, it is not suitable for photographing a dark object.
An example of a high telecentric zoom lens system is disclosed in Japanese Laid-open Patent Application H3-71686. This zoom lens system, however, does not have a large field angle at the wide-angle end.